The invention relates to a method and a device for projecting sound sources onto loudspeakers in order, in particular, to permit spatial reproduction of the sound sources.
It is known from the MPEG-2 Standard ISO 13818 to aim at a spatial representation by means of multichannel stereophony, also called surround sound, for audio reproduction. Six channels are provided in this case for the multichannel sound, of which three channels (left, centre, right) are arranged in space in front of the listener, two channels (left surround, right surround) are arranged in space behind the listener, and a sixth channel is provided for reproducing low-pitched tones for special effects. The sound channels are matrixed in order, on the one hand, to ensure reverse compatibility with MPEG-1 audio signals and, on the other hand, also to render satisfactory reproduction possible, if instead of a complete surround-sound loudspeaker configuration only a pair of loudspeakers are present. In this case, the calculated stereosignals are transmitted as MPEG-1-compatible stereosignal and the remaining signals as additional data.
It is the object of the invention to specify a method for spatial reproduction of virtual sound sources. This object is achieved by means of the method specified in claim 1.
It is the further object of the invention to specify a device for applying the method according to the invention. This object is achieved by means of the device specified in claim 8.
In order to reproduce an audio signal, the latter frequently has to be projected onto the positions of the existing loudspeakers. A few projections may be mentioned here by way of example:
a) The projection of a mono signal onto a pair of stereo loudspeakers.
b) The projection of a 3/2-signal (3 loudspeakers in front/2 loudspeakers behind) onto a 2/2 loudspeaker arrangement.
c) The projection of a signal with the position 3 m away, 30xc2x0 left, 10xc2x0 high onto a loudspeaker ring which comprises 8 loudspeakers at a distance of 2 m with a respective 45xc2x0 spacing.
d) The projection of 2 sound sources in the room onto 2 loudspeakers.
It is desirable not to have to be fixed on a specific configuration for the transmission of an audio signal. However, the problem arises in this case that there is an unlimited number of possible combinations.
In principle, the method according to the invention for projecting sound sources onto loudspeakers consists in that the sound sources are interpreted as acoustic objects, an acoustic object consisting in that in addition to the audio signal a sound source is assigned an item of spatial information which specifies a virtual, spatial position of the sound source.
The audio signal is advantageously processed as a function of the associated item of spatial information in order to reproduce an acoustic object.
In this case, the spatial position of the loudspeakers is preferably additionally considered, the virtual distance of the sound source from the loudspeaker being calculated from the spatial information and the position of the loudspeakers, and separate processing of the audio signal for each of the loudspeakers being performed for an acoustic object.
It is, furthermore, advantageous when one or more of the following parameters are considered when processing the audio signals:
amplitude attenuation, for example by damping or diffraction,
a different propagation time for the various acoustic objects and loudspeakers,
consideration of the dependence of the loudspeaker level on the spatial arrangement by means of the outer ear function.
In this case, the processing of the audio signals can be further improved when the frequency dependence of the parameters is also considered.
The mathematical functions required for considering the parameters such as, for example, an attenuation function are preferably transmitted and/or stored as a function of the distance and/or the angle of deflection.
It is particularly advantageous when the data of an acoustic object are stored and/or transmitted by means of a compressed data stream in accordance with the MPEG-4 Standard.
In principle, the device according to the invention for projecting sound sources onto loudspeakers consists in that an arithmetic unit is provided which calculates the distance of the virtual acoustic objects from the respective loudspeakers from an item of spatial information transmitted with the audio signal and the actual position of the loudspeakers.
In this case, a memory is preferably provided in which the respective loudspeaker positions and/or mathematical functions for considering parameters are stored.
It is advantageous to provide nxc3x97k actuators for n acoustic objects and k loudspeakers, an actuator carrying out processing of an audio signal with reference to one of the loudspeakers.
In this case, a frequency dependence of the parameters is preferably also considered by the actuators, the signals firstly being resolved into frequency bands by a split filter (10), the individual frequency bands then being processed individually, and the processed frequency bands subsequently being recombined by a merge filter (12).
It is particularly advantageous when the split filter and/or the merge filter are part of an audio decoder which is present in any case.
Furthermore, one or more directional microphones can preferably be provided which are used to measure the loudspeaker position.
The directional microphones are preferably integrated in a remote control.